Before You Begin

Before you begin configuring a J-series or SRX-series device for CoS, complete the following tasks:

If you do not already have a basic understanding of CoS, read Class-of-Service Overview.
Determine whether the device needs to support different traffic streams, such as voice or video. If so, CoS helps to make sure this traffic receives more than basic best-effort packet delivery service.
Determine whether the device is directly attached to any applications that send CoS-classified packets. If no sources are enabled for CoS, you must configure and apply rewrite rules on the interfaces facing the sources.
Determine whether the device must support assured forwarding (AF) classes. Assured forwarding usually requires random early detection (RED) drop profiles to be configured and applied.
Determine whether the device must support expedited forwarding (EF) classes with a policer. Policers require you to apply a burst size and bandwidth limit to the traffic flow, and set a consequence for packets that exceed these limits—usually a high loss priority, so that packets exceeding the policer limits are discarded first.